Wireless communication systems are well known in the art. Generally, such systems comprise communication stations, i.e. wireless transmit/receive units (WTRUs), which transmit and receive wireless communication signals between each other. Depending upon the type of system, communication stations typically are one of two types: base stations or subscriber WTRUs, which include mobile units.
In order to provide global connectivity for wireless systems, standards have been developed and are being implemented. One current standard in widespread use is known as Global System for Mobile Telecommunications (GSM). This is considered as a so-called Second Generation mobile radio system standard (2G) and was followed by its revision (2.5G). GPRS (General Packet Radio Service) and EDGE (Enhanced Data rates for Global Evolution) are examples of 2.5G technologies that offer relatively high speed data service on top of (2G) GSM networks. Each one of these standards sought to improve upon the prior standard with additional features and enhancements. In January 1998, the European Telecommunications Standard Institute—Special Mobile Group (ETSI SMG) agreed on a radio access scheme for Third Generation Radio Systems called Universal Mobile Telecommunications Systems (UMTS). To further implement the UMTS standard, the Third Generation Partnership Project (3GPP) was formed in December 1998. 3GPP continues to work on a common third generational mobile radio standard.
A typical UMTS system architecture in accordance with current 3GPP specifications is depicted in FIG. 1. The UMTS network architecture includes a Core Network (CN) interconnected with a UMTS Terrestrial Radio Access Network (UTRAN) via an interface known as Iu which is defined in detail in the current publicly available 3GPP specification documents. The UTRAN is configured to provide wireless telecommunication services to users through wireless transmit receive units (WTRUs), known as User Equipments (UEs) in 3GPP, via a radio interface known as Uu. The UTRAN has one or more Radio Network Controllers (RNCs) and base stations, known as Node Bs in 3GPP, which collectively provide for the geographic coverage for wireless communications with UEs. One or more Node Bs are connected to each RNC via an interface known as Iub in 3GPP. The UTRAN may have several groups of Node Bs connected to different RNCs; two are shown in the example depicted in FIG. 1. Where more than one RNC is provided in a UTRAN, inter-RNC communication is performed via an Iur interface.
Communications external to the network components are performed by the Node Bs on a user level via the Uu interface and the CN on a network level via various CN connections to external systems.
A CN is responsible for routing information to its correct destination. For example, the CN may route voice traffic from a UE that is received by the UMTS via one of the Node Bs to a public switched telephone network (PSTN) or packet data destined for the Internet. In 3GPP, the CN has six major components: 1) a serving General Packet Radio Service (GPRS) support node; 2) a gateway GPRS support node; 3) a border gateway; 4) a visitor location register; 5) a mobile services switching center; and 6) a gateway mobile services switching center. The serving GPRS support node provides access to packet switched domains, such as the Internet. The gateway GPRS support node is a gateway node for connections to other networks. All data traffic going to other operator's networks or the internet goes through the gateway GPRS support node. The border gateway acts as a firewall to prevent attacks by intruders outside the network on subscribers within the network realm. The visitor location register is a current serving networks ‘copy’ of subscriber data needed to provide services. This information initially comes from a database which administers mobile subscribers. The mobile services switching center is in charge of ‘circuit switched’ connections from UMTS terminals to the network. The gateway mobile services switching center implements routing functions required based on current location of subscribers. The gateway mobile services switching center also receives and administers connection requests from subscribers from external networks.
The RNCs generally control internal functions of the UTRAN. The RNCs also provides intermediary services for communications having a local component via a Uu interface connection with a Node B and an external service component via a connection between the CN and an external system, for example overseas calls made from a cell phone in a domestic UMTS.
Typically a RNC oversees multiple base stations, manages radio resources within the geographic area of wireless radio service coverage serviced by the Node Bs and controls the physical radio resources for the Uu interface. In 3GPP, the Iu interface of an RNC provides two connections to the CN: one to a packet switched domain and the other to a circuit switched domain. Other important functions of the RNCs include confidentiality and integrity protection.
In general, the primary function of base stations, such as Node Bs, is to provide a radio connection between the base stations' network and the WTRUs. Typically a base station emits common channel signals allowing non-connected WTRUs to become synchronized with the base station's timing. In 3GPP, a Node B performs the physical radio connection with the UEs. The Node B receives signals over the Iub interface from the RNC that control the radio signals transmitted by the Node B over the Uu interface. The Uu radio interface of a 3GPP communications system uses Transport Channels (TrCH) for transfer of user data and signaling between UEs and Node Bs. The channels are generally designated as Shared Channels, i.e. channels concurrently available to more than one UE, or dedicated channels (DCHs) which are assigned for use with a particular UE during a wireless communication.
In many wireless communication systems, adaptive transmission power control algorithms are used to control the transmission power of WTRUs. In such systems, many WTRUs may share the same radio frequency spectrum. When receiving a specific communication, all other communications transmitted on the same spectrum cause interference to the specific communication. As a result, increasing the transmission power level of one communication degrades the signal quality of all other communications within that spectrum. However, reducing the transmission power level too far results in undesirable received signal quality, such as measured by signal to interference ratios (SIRs) at the receivers.
Various methods of power control for wireless communication systems are well known in the art. An example of an open loop power control transmitter system for a wireless communication system is illustrated in FIG. 2. The purpose of such systems is to rapidly vary transmitter power in the presence of a fading propagation channel and time-varying interference to minimize transmitter power while insuring that data is received at the remote end with acceptable quality.
In communication systems such as Third Generation Partnership Project (3GPP) Time Division Duplex (TDD) and Frequency Division Duplex (FDD) systems, multiple shared and dedicated channels of variable rate data are combined for transmission. In 3GPP wideband CDMA (WCDMA) systems, power control is used as a link adaptation method. Dynamic power control is applied for dedicated physical channels (DPCH), such that the transmit power of the DPCHs is adjusted to achieve a quality of service (QoS) with a minimum transmit power level, thus limiting the interference level within the system.
One conventional approach for power control is to divide transmission power control into separate processes, referred to as outer loop power control (OLPC) and inner loop power control (ILPC). The power control system is generally referred to as either open or closed dependent upon whether the inner loop is open or closed. Typically for 3GPP systems for uplink communications, the outer loops of both types of systems are closed loops. The inner loop in an example WCDMA open loop type of system illustrated in FIG. 2 is an open loop.
In outer loop power control, the power level of a specific transmitter is typically based on a target, such as a target SIR value. As a receiver receives the transmissions, the quality of the received signal is measured. In 3GPP systems, the transmitted information is sent in units of transport blocks (TBs) and the received signal quality can be monitored on a block error rate (BLER) basis. The BLER is estimated by the receiver, typically by a cyclic redundancy check (CRC) of the data. This estimated BLER is compared to a target quality requirement, such a target BLER, representative of QoS requirements for the various types of data services on the channel. Based on the measured received signal quality, a target SIR adjustment control signal is generated and the target SIR is adjusted in response to these adjustment control signals.
In inner loop power control, the receiver compares a measurement of the received signal quality, such as SIR, to a threshold value. If the SIR exceeds the threshold, a transmit power command (TPC) to decrease the power level is sent. If the SIR is below the threshold, a TPC to increase the power level is sent. Typically, the TPC is multiplexed with data in a dedicated channel to the transmitter. In response to received TPC, the transmitter changes its transmission power level.
Conventionally, the outer loop power control algorithm in a 3GPP system sets an initial target SIR for each coded composite transport channel (CCTrCH) based on a required target BLER, using a fixed mapping between BLER and SIR, assuming a particular channel condition. A CCTrCH is commonly employed for transmitting various services on a physical wireless channel by multiplexing several transport channels (TrCHs), each service on its own TrCH. In order to monitor the BLER level on a CCTrCH basis, a reference transport channel (RTrCH) may be selected among the transport channels multiplexed on the considered CCTrCH.
Uplink power control for dedicated channels transmitted by WTRUs in a 3GPP system typically consists of a closed outer loop and an open inner loop such as is the example illustrated in FIG. 2. The closed outer loop is responsible for determination of a SIR target for the uplink transmission made by a particular WTRU. The initial value of SIR target is determined by a Controlling RNC (C-RNC), and then can be adjusted by a Serving RNC (S-RNC) based on measurement of uplink CCTrCH quality. The S-RNC then sends the update of the SIR target to the WTRU. The open inner loop calculates the uplink transmit power by the WTRU measuring the serving cell's P-CCPCH received signal code power (RSCP) every frame and calculating pathloss between the Node B and the WTRU. Based on the pathloss and the UTRAN signaled values of SIR target and UL Timeslot interference signal code power (ISCP) of the UL CCTrCH, the WTRU calculates the transmit power of a dedicated physical channel (PDPCH).
Each DPCH (DPCHi) of the CCTrCH is then separately weighted by a weight factor γi which compensates for the different spreading factors used by the different DPCHs. The DPCHs in each timeslot are then combined using complex addition.
After combination of physical channels, the CCTrCH gain factor β is applied. The gain factor compensates for differences in transmit power requirements for different TFCs assigned to the CCTrCH: each TFC represents a different combination of data from each of the transport channels of the Coded Composite Transport Channel (CCTrCH). Each combination can result in a different amount of repetition or puncturing applied to each TrCH in the CCTrCH. Since puncturing/repetition affects the transmit power required to obtain a particular signal to noise ratio (Eb/N0), the gain factor applied depends on the TFC being used, i.e. each TFC of the CCTrCH has its own gain factor. The value for gain factor βj applies to the jth TFC of the CCTrCH. This process is illustrated conceptually in FIG. 3 where, for example, the dedicated channels DPCH1 and DPCH2 carry data of the jth TFC of TrCHs.
The βj value can be explicitly signaled to the WTRU for each TFCj, or the radio resource control (RRC) in the RNC can indicate that the UE should calculate βj for each TFC based on an explicitly signaled value of a reference TFC. This calculation is conventionally done based on the rate matching parameters and the number of resource units needed by the given TFCj and the reference TFC, where a resource unit is defined, for example, as one SF16 code. For physical channel configurations with SF16 codes only, the number of resource units (RUs) is equal to the number of codes. For configurations with codes that are not all SF16, the number of RUs is the equivalent number of SF16 codes. Equivalency for each of the spreading factors is as follows: 1 SF8 code=2 RUs, 1 SF4 code=4 RUs, 1 SF2 code=8 RUs, 1 SF1 code=16 RUs.
The first method is referred to as “signaled gain factors” and the second as “computed gain factors”.
The conventional method for a subscriber WTRU to calculate β factors based on a reference TFC is provided is as follows:
Let βref denote the signaled gain factor for the reference TFC and βj denote the gain factor used for the j-th TFC.
Define the variable:
      K    ref    =            ∑      i        ⁢                  RM        i            ×              N        i                            where RMi is the semi-static rate matching attribute for transport channel i, Ni is the number of bits output from the radio frame segmentation block for transport channel i and the sum is taken over all the transport channels i in the reference TFC.        
Similarly, define the variable
      K    j    =            ∑      i        ⁢                  RM        i            ×              N        i                            where the sum is taken over all the transport channels i in the j-th TFC.        
Moreover, define the variable
      L    ref    =            ∑      i        ⁢          1              SF        i                            where SFi is the spreading factor of DPCH i and the sum is taken over all DPCH i used in the reference TFC.        
Similarly, define the variable
      L    j    =            ∑      i        ⁢          1              SF        i                            where the sum is taken over all DPCH i used in the j-th TFC.        
The gain factor βj for the j-th TFC is then conventionally computed as:
      β    j    =                              L          ref                          L          j                      ×                            K          j                          K          ref                    
Instead of sending a reference TFC, the values of the gain factor for each TFC can be determined in the RNC and sent to the WTRU. However, the current standards do not define how to determine the signaled gain factor values that are to be sent to the WTRUs. The inventors have recognized that the calculation of gain factors for TFCs can be improved by making them proportional to the gain factor applicable to a reference TFC. This improvement has applicability for both “signaled gain factors” and “computed gain factors”.
Another problem arising in conventional system relates to uplink power control maintenance during reconfiguration. When physical channel reconfiguration changes the spreading factors used for a CCTrCH, puncturing/repetition for each TFC may be different before and after the reconfiguration. Since conventionally the gain factors depend on the relative puncturing/repetition among the TFCs, the gain factors used before reconfiguration may be misaligned with the puncturing/repetition after reconfiguration.
The inventors have recognized that this leads to the need for power control to re-converge based on the new puncturing/repetition of the TFCs. If new gain factors are computed or selected which do not result in the same output power levels after reconfiguration relative to puncturing/repetition, re-convergence is required. To reduce the need for re-convergence, the inventors have recognized that it would be advantageous to:                select a reference TFC and a reference gain factor value which will be appropriate before and after reconfiguration;        select a new reference TFC to use after reconfiguration (reference gain factor remains the same before and after reconfiguration);        select a new reference gain factor to use after reconfiguration (reference TFC remains the same before and after reconfiguration); and/or        select a new SIR target to use after reconfiguration.        